Humidity control algorithm

ABSTRACT

A system and method is provided to control the operation of an HVAC system to remove humidity from an indoor air environment without cooling the indoor air environment. The system includes a thermostat that operates the HVAC system to remove humidity when the sensed humidity falls below a humidity set point. After operation of the HVAC system, the thermostat monitors whether the temperature within the indoor air environment falls due to the operation of the HVAC system. If the temperature within the indoor air environment falls consistently, the humidity control algorithm determines that the HVAC system cannot operate without cooling and prevents future operation of the HVAC system to provide only dehumidification. If, however, the humidity control algorithm determines that the HVAC system can operate to dehumidify without cooling, the humidity control algorithm operates the HVAC system accordingly.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from U.S. Provisional Patent Application Ser. No. 60/797,633 filed on May 4, 2006.

BACKGROUND OF THE INVENTION

Recently, there have been many advancements in the operation of HVAC systems regarding humidity control. In particular, there currently exist HVAC systems that are capable of removing humidity from the air without cooling the air. In many of these systems, humidity is removed from the air and, once the humidity has been removed, the dehumidified air is heated enough such that the air returned to the enclosed environment has not been cooled.

As with many technological advances, the controls and control algorithms for HVAC systems have lagged the advances in the physical equipment. Presently, thermostats or HVAC controls only call for dehumidification when there is also a call for cooling or when the current temperature of the indoor air environment is close to the cooling temperature set point such that a small amount of over-cooling may be allowed. However, currently available thermostats and HVAC controllers are not capable of operating the HVAC system as a dehumidifier independently when the temperature within the building is below the cooling temperature set point such that a demand for cooling is not indicated.

In addition, in many applications, a thermostat or HVAC controller may be installed after the HVAC system or the thermostat may be an upgrade to the original thermostat installed with the HVAC system. In these situations, the thermostat will not know the operational characteristics of the HVAC system or appreciate the HVAC system's ability to dehumidify the air without additional cooling. Thus, the thermostat may not utilize the ability of the HVAC system to dehumidify the air within the indoor air environment being controlled.

Therefore, a need exists for an improved thermostat and HVAC controller that takes advantage of the advancements in HVAC systems to remove humidity from the air while monitoring for a decrease in temperature.

SUMMARY OF THE INVENTION

The present invention generally relates to a system and method for controlling the operation of an HVAC system that is capable of dehumidifying and cooling an indoor air environment. The method and system generally includes a thermostat positioned within the building or room in which the HVAC system operates to control the temperature and humidity of the indoor air environment. The thermostat is in communication with the HVAC system such that control signals from the thermostat can be used to control the operation of the HVAC system.

In one embodiment, the thermostat senses the humidity in a location that has the indoor air environment controlled by the HVAC system. If the humidity in the location is greater than a humidity set point, the thermostat activates the HVAC system to begin removing humidity from the indoor air environment. At the time the HVAC system is initially activated, the thermostat senses the temperature in the location having the indoor air environment controlled by the HVAC system.

Following activation of the HVAC system, the thermostat continues to monitor the temperature in the location having the indoor air temperature controlled by the HVAC system and compares the starting temperature to the current temperature. If the HVAC system is not capable of dehumidifying the indoor air environment without also cooling the indoor air environment, the current temperature will fall below the starting temperature. The thermostat continues to monitor the difference between the current temperature and the starting temperature and deactivates the HVAC system when the current temperature falls below the starting temperature by more than a temperature limit.

In this manner, the thermostat operates the HVAC system without knowing whether the HVAC system is capable of dehumidifying without cooling. If the thermostat learns that the HVAC system is not capable of dehumidifying without cooling, the thermostat will discontinue activating the HVAC system for dehumidification purposes only in the future. In this manner, the thermostat can learn the operational characteristics of the HVAC system and utilize performance characteristics of the HVAC system to provide for improved cooling and dehumidification functions.

In one embodiment, the thermostat senses the starting temperature in the location near the thermostat and within a building or room having the indoor air environment controlled by the HVAC system. In this embodiment, both the starting temperature and the current temperature are temperatures measured near the thermostat. In an alternate embodiment, the system includes a temperature probe positioned to sense the temperature of the air flow leaving the HVAC system. In this alternate embodiment, the temperature probe relays the current temperature of the air flow from the HVAC system to the thermostat such that the thermostat can compare the temperature of the air flow leaving the HVAC system to a starting temperature that is related to the temperature of the indoor air environment being controlled by the HVAC system. The use of a temperature probe to sense the air flow from the HVAC system provides a more immediate indication of whether the HVAC system is capable of operation to remove humidity without cooling the indoor air environment.

As described above, current improvements in dehumidifiers are generally centered around the equipment's ability to remove humidity from the air without cooling the air. This is accomplished by different manufacturers in different ways, such as reheating the air after the dehumidification process. Because the dehumidifier is not cooling the air, it is possible to run the dehumidification equipment when there is a call for dehumidification but not a call for cooling. One implementation of this would be to observe the room temperature at the start of the call for dehumidification and monitor that temperature as the call continues. If the temperature begins to fall during the call for dehumidification by a pre-set temperature differential, the call for dehumidification will be terminated. Otherwise, the call will continue until the dehumidifier has satisfied the demand for dehumidification.

Alternatively, the method could be further enhanced by providing a temperature probe at an outlet vent for the HVAC system. By observing the temperature at the outlet vent, rather than at the thermostat or control itself, the thermostat could respond faster to equipment that does cool and prevent undercooling, and thus not leave the homeowner uncomfortable. The thermostat could also, after several cycles, “remember” that the equipment is capable of dehumidification without cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings:

FIG. 1 is a schematic illustration of the thermostat control as used with an HVAC system;

FIG. 2 is a schematic illustration of a second, alternate embodiment of the thermostat control used with an HVAC system;

FIG. 3 is a state diagram showing the specific transitions that apply to a dehumidification-controlling algorithm implemented by the thermostat shown in FIGS. 1 and 2; and

FIG. 4 is a flowchart illustrating the operational decision made by the dehumidification-controlling algorithm implemented by the thermostat shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, thereshown is a thermostat 10 connected to an HVAC system 12 that includes both a dehumidifier 14 and an air conditioner 16. The HVAC system includes a blower 18 that draws a supply of air through an inlet duct 20 from the indoor air environment being conditioned through the HVAC system 12 and out of an outlet duct 22 for return to the home.

The thermostat 10 includes a user input 24 that allows the home occupant to enter the desired set point temperature for heating and cooling. Further, the user input 24 allows the home occupant to enter a desired set point for the relative humidity within the home. The thermostat 10 receives a temperature signal from the temperature sensor 26 and a humidity signal from the humidity sensor 28. Typically, the temperature sensor 26 and humidity sensor 28 are incorporated directly into the thermostat 10. However, the temperature sensor 26 and humidity sensor 28 can be located remotely from the thermostat and communicate to the thermostat using either a wired or wireless connection while operating within the scope of the present invention.

During normal operation, the thermostat 10 monitors the temperature from the temperature sensor 26 and compares the current temperature to the cooling temperature set point. If the room temperature exceeds the cooling set point, the thermostat 10 sends a signal to the air conditioner 16 and the blower 18 to begin operation. Once the air conditioner 16 has begun operation, the thermostat 10 monitors the current room temperature from the signal received from the temperature sensor 26 and continues to operate the air conditioner 16 until the room temperature falls below the cooling temperature set point minus an offset value. As an example, if the cooling set point is selected to be 70°, the thermostat 10 will continue to operate the air conditioner until the temperature sensor 26 returns a sensed temperature of 68°, which is a 2° offset below the cooling set point.

In presently available HVAC systems, the thermostat 10 will turn on the dehumidifier 14 when both the relative humidity of the indoor air environment exceeds the humidity set point and the temperature of the indoor air environment calls for cooling. Some systems will also activate the dehumidifier 14 when the temperature within the home is very near the cooling set point. In prior HVAC systems, the operation of the dehumidifier 14 resulted in cooling of the air being drawn from the house such that operation of the dehumidifier 14 would result in cooling of the air within the home. For this reason, the thermostat 10 allowed for operation of the dehumidifier 14 only when there was a call for cooling or when the current temperature was very close to the cooling set point to prevent overcooling of the home. However, currently available HVAC systems 12, such as shown in FIG. 1, include dehumidifiers 14 that can be operated without cooling the air within a home.

In addition to the HVAC system shown in FIG. 1, currently available HVAC systems 50, such as shown in FIG. 2, are available that include an additional heater 52 that is positioned downstream from the dehumidifier 14. Since the operation of the dehumidifier 14 results in a reduction in the temperature of the air flow, the heater 52 can be operated to reheat the air flow after the dehumidification process. The net result of the operation of the dehumidifier 14 and the heater 52 is that the output air flow has the same temperature as the input but with a significant reduction in the humidity of the air flow. The operation of the HVAC system 50 to remove humidity without cooling the indoor air environment requires operation of both the dehumidifier 14 and the heater 52 to prevent a reduction in the temperature of the air within the indoor air environment. As with the embodiment shown in FIG. 1, the thermostat 10 controls the operation of the entire HVAC system 50, including the blower 18.

In accordance with the present invention, upon a dehumidification demand without a request for cooling, the thermostat 10 will send a signal to the dehumidifier 14 and the blower 18 to begin operation when the relative humidity within the home exceeds the humidity set point. During operation of the dehumidifier 14 and the blower 18, the thermostat 10 will monitor the temperature within the home through the use of the temperature sensor 26. If the temperature within the home begins to fall during the operation of the dehumidifier 14 and the blower 18, the call for dehumidification will be terminated to prevent overcooling of the home. Since the thermostat 10 may be connected to an HVAC system that does not include a dehumidifier 14 that can operate without cooling the air, the thermostat 10 must monitor the temperature within the home during operation of the dehumidifier to prevent overcooling.

If the thermostat 10 determines that the dehumidifier 14 cannot be operated without cooling the air, the thermostat 10 will “remember” that the dehumidifier 14 is not capable of dehumidification without cooling and will no longer operate the dehumidifier 14 when the temperature within the home is below the cooling set point. However, if the thermostat 10 determines that the operation of the dehumidifier 14 and the blower 18 does not result in cooling within the home, the thermostat 10 will continue to operate the dehumidifier 14 until the relative humidity within the home falls below the humidity set point. In this manner, the thermostat 10 is able to “learn” the type of equipment contained within the HVAC system 12 and operate the dehumidifier 14 accordingly.

In a most preferred embodiment of the invention, the HVAC systems 12, 50 include a temperature probe 29 positioned within the outlet duct 22 leaving the HVAC system 12 or within an outlet vent. The temperature probe 29 is directly connected to the thermostat 10 and provides a direct measurement of the temperature of the air leaving the HVAC system 12. The thermostat 10 can observe the temperature at the outlet duct 22 to immediately determine if the dehumidifier 14 is cooling the air along with the dehumidification process. If the thermostat 10 determines that the air is being cooled and dehumidified, the thermostat 10 will “remember” that the dehumidifier 14 is not capable of dehumidification without cooling and will only operate the dehumidifier 14 when cooling is also required. However, if the temperature probe 29 indicates that the air is not being cooled, the thermostat 10 will continue to operate the dehumidifier 14 when the relative humidity exceeds the humidity set point. In this manner, the thermostat 10 can “learn” the type of HVAC system 12 it is connected to and operate the dehumidifier 14 accordingly.

Referring now to FIG. 3, thereshown is a state diagram showing the specific transitions that apply to the dehumidification-controlling algorithm implemented in a thermostat with internal, or external, realization of relative humidity levels and desired limits. As indicated in FIG. 3, when the thermostat 10 is in the NO MODE ON state 30, the thermostat will transition to the DEHUMIDIFY MODE ON state 32 upon a dehumidification demand, as shown in box 34. Upon receiving a demand for dehumidification, the control algorithm will set the start temperature equal to the current temperature within the home, as also indicated in box 34. Alternatively, in an HVAC system that includes a temperature probe positioned within the outlet duct, the start temperature can be set equal to the current temperature received from the temperature probe.

As the dehumidification continues in state 32, the control algorithm determines whether the start temperature minus the current temperature is greater than a preselected temperature limit. If the difference between the current temperature and the start temperature exceeds the temperature limit, indicating that the dehumidifier cools the air while removing the humidity, or if there is no longer a demand for dehumidification, as shown in box 36, the control algorithm returns to the NO MODE ON state 30. As an example, if the temperature limit is set at 4°, the algorithm will turn off the dehumidifier once the difference between the start temperature and the current temperature exceed the 4° temperature limit, thereby indicating that the dehumidifier 14 is cooling the air returned to the home.

When the control algorithm is in the dehumidification mode 32, the algorithm will move to the COOL MODE ON 38 upon a call for cooling, as indicated by box 40. The algorithm will return back to the DEHUMIDIFY MODE ON 32 when the call for cooling has been satisfied but the dehumidification demand remains, as indicated by box 42. Alternatively, if the cooling and dehumidification demands are both satisfied, the algorithm will return to the NO MODE ON state 30, as indicated by box 44.

In an HVAC system including the temperature probe 29, the thermostat will set the start temperature to equal the temperature of the air flowing over the temperature probe 29 when the HVAC is first activated. The control algorithm will monitor for a change in the temperature at the temperature probe 29 and will turn off the dehumidifier if the temperature changes more than a selected limit.

FIG. 4 illustrates a flowchart setting forth the operational sequence performed by the humidity control algorithm that is present within the thermostat or HVAC controller 10. FIG. 4 simply illustrates the humidity control algorithm and does not describe the entire operation of the thermostat 12 for controlling the operation of the HVAC system.

As illustrated in FIG. 4, the humidity control algorithm initially determines at step 54 whether the humidity sensed by the humidity sensor 28 is greater than a humidity set point. In such a case, the indoor air environment being controlled by the HVAC system has a humidity level higher than the humidity set point entered by the user.

If the sensed humidity is greater than the humidity set point, the humidity control algorithm sets the start temperature equal to the current temperature, as indicated in step 56. As described previously, the start temperature can be either the temperature received from the temperature sensor 26 or from the temperature probe 29 positioned within the outlet duct leading from the HVAC system. In either case, the thermostat sets the start temperature to be equal to the current temperature prior to activation of the HVAC system.

Once the start temperature has been set equal to the current temperature, the thermostat activates the HVAC system, as shown in step 58. As described previously, the activation of the HVAC system may include only the activation of the dehumidifier 14 and the blower 18. Alternatively, in the embodiment shown in FIG. 2, the activation of the HVAC system to remove humidity from the indoor air environment may also result in the activation of the heater 52. In accordance with the humidity control algorithm presented by the present invention, the thermostat initially activates the HVAC system without the thermostat knowing the type of HVAC system to which it is connected.

After the HVAC system has been activated to remove humidity from the indoor air environment, the thermostat monitors the current temperature in step 60. In one embodiment described previously, the current temperature is measured by the temperature sensor 26 while in another embodiment, the current temperature is measured by the temperature probe 29. In either embodiment, the current temperature is continuously monitored after activation of the HVAC system 58.

As indicated in step 62, the humidity control algorithm subtracts the current temperature from the start temperature and determines whether the difference between the start temperature and the current temperature is greater than a temperature limit. As an example, if the HVAC system is not capable of removing humidity from the indoor air environment without cooling, the current temperature will begin to drop after activation of the HVAC system, thus increasing the difference between the current temperature and the start temperature. Preferably, the temperature limit will be selected as a value that allows for a small variation between the current temperature and the start temperature, such as for an illustrative example only, 3°.

If the current temperature remains close enough to the start temperature such that the difference does not exceed the temperature limit, the humidity control algorithm then determines if the sensed humidity is less than the humidity set point in step 64. If the sensed humidity is not yet below the humidity set point, the algorithm returns to step 58 and continues to activate the HVAC system to remove humidity.

However, if the sensed humidity is now below the humidity set point, the HVAC system is deactivated in step 66 and the system returns to the starting point for the algorithm.

Returning now to step 62, if the humidity control algorithm determines that the temperature difference between the current temperature and the start temperature is greater than the temperature limit, the humidity control algorithm deactivates the HVAC system in step 68. If the HVAC system is incapable of removing humidity without cooling, the difference between the starting temperature and the current temperature will most likely be due to this inability of the HVAC system. However, it is possible that the difference between the start temperature and the current temperature may be due to other changes within the indoor air environment and not based solely upon the inability of the HVAC system to dehumidify without cooling. Thus, in step 70, the humidity control algorithm determines whether the cooling of the indoor air environment upon activation of the dehumidifier is habitual. It is contemplated that the determination of whether the cooling is habitual in step 70 can be carried out using many different techniques. These techniques may count the number of times the start temperature and current temperature vary greater than the temperature limit as compared to the number of times the dehumidification function has been carried out by the humidity control algorithm.

If the humidity control algorithm determines that the HVAC system is incapable of providing dehumidification without cooling, the algorithm is deactivated in step 72. This prevents the thermostat from activating the HVAC system to provide only dehumidification when the HVAC system is incapable of operating in such a manner.

If in step 70 the humidity control algorithm determines that the cooling after activation of the HVAC system is not habitual, the algorithm creates a delay in step 74 and then returns to the start, as indicated in step 76. The reason for the delay and the return to the start is so that the temperature within the indoor air environment can return to a steady state prior to the humidity control algorithm operating in step 54.

As can be understood by the above description, a thermostat or HVAC controller that operates utilizing the humidity control algorithm described includes internal operating methods that allow the thermostat to identify whether the HVAC system that it is controlling includes the ability to dehumidify air without providing additional cooling. Thus, a thermostat operating under the humidity control algorithm is capable of being installed in a system and determining whether the system can be operated to simply remove humidity, since the system is capable of learning as it operates. 

1. A method of operating an HVAC system capable of dehumidifying and cooling an indoor air environment comprising the steps of: sensing the humidity in a location having the indoor air environment controlled by the HVAC system; comparing the sensed humidity to a humidity set point; activating the HVAC system when the sensed humidity exceeds the humidity set point; sensing a starting temperature in the location having the indoor air environment controlled by the HVAC system upon activation of the HVAC system; monitoring a current temperature in the location having the indoor air temperature controlled by the HVAC system; comparing the starting temperature to the current temperature; and deactivating the HVAC system when the current temperature falls below the starting temperature by more than a temperature limit.
 2. The method of claim 1 wherein the HVAC system is deactivated even when the sensed humidity exceeds the humidity set point when the change in temperature exceeds the temperature limit.
 3. The method of claim 1 wherein the HVAC system is activated when the sensed humidity exceeds the humidity threshold and the current temperature is below a temperature set point.
 4. The method of claim 3 wherein the temperature set point and the humidity set point are user selectable.
 5. The method of claim 1 wherein the step of activating the HVAC system includes at least activating a dehumidifier and activating a blower to operate in concert with the dehumidifier.
 6. The method of claim 1 wherein the HVAC system is deactivated when the current temperature falls below the start temperature by more than the temperature limit and the current temperature is below the temperature set point.
 7. A method of operating an HVAC system capable of dehumidifying and cooling an indoor air environment comprising the steps of: sensing the humidity in a location having the indoor air environment controlled by the HVAC system; comparing the sensed humidity to a humidity set point; activating the HVAC system when the sensed humidity exceeds the humidity set point; sensing a starting temperature of the air flow from the HVAC system upon activation of the HVAC system; monitoring a current temperature of the air flow from the HVAC system after activation of the HVAC system; comparing the current temperature of the air flow to the starting temperature; and deactivating the HVAC system when the current temperature of the air flow falls below the starting temperature by more than a temperature limit.
 8. The method of claim 7 wherein the HVAC system is deactivated even when the sensed humidity exceeds the humidity set point when the current air flow temperature falls below the starting temperature by more than the temperature limit.
 9. The method of claim 7 wherein the HVAC system is activated when the sensed humidity exceeds the humidity threshold and a current temperature of the indoor air environment controlled by the HVAC system is below a temperature set point.
 10. The method of claim 9 wherein the temperature set point and the humidity set point are user selectable.
 11. The method of claim 7 wherein the step of activating the HVAC system includes at least activating a dehumidifier and activating a blower to operate in concert with the dehumidifier.
 12. The method of claim 7 wherein the HVAC system is deactivated when the air flow temperature falls below the starting temperature by more than the temperature limit and the current temperature is below the temperature set point.
 13. A method of operating a thermostat to control the activation of an HVAC system, the method comprising the steps of: sensing the humidity of an indoor air environment controlled by the HVAC system; comparing the sensed humidity to a humidity set point entered into the thermostat; activating the HVAC system when the sensed humidity exceeds the humidity set point; sensing a starting temperature related to the indoor air environment upon activation of the HVAC system; monitoring a current temperature related to the indoor air environment after activation of the HVAC system; comparing the current temperature to the starting temperature; and deactivating the HVAC system when the current temperature falls below the starting temperature by more than a temperature limit.
 14. The method of claim 13 wherein the current temperature is the temperature of the indoor air environment controlled by the HVAC system.
 15. The method of claim 14 wherein the current temperature is sensed by a temperature sensor within the thermostat.
 16. The method of claim 14 wherein the HVAC system is deactivated even when the sensed humidity exceeds the humidity set point when the current temperature falls below the starting temperature by more than the temperature limit.
 17. The method of claim 13 wherein the temperature set point and the humidity set point are user settable in the thermostat.
 18. The method of claim 13 wherein the current temperature is the temperature of the air flow from the blower of the HVAC system.
 19. The method of claim 18 further comprising the steps of: positioning an air flow temperature probe to detect the temperature of the air flow from the HVAC system; and communicating the air flow temperature from the air flow temperature probe to the thermostat.
 20. A system for controlling the operation of an HVAC system capable of dehumidifying and cooling an indoor air environment, the system comprising: a thermostat positionable within the indoor air environment to be controlled by the HVAC system, the thermostat having operational output in communication with the HVAC system; a temperature sensor coupled to the thermostat and operable to determine the air temperature of the indoor air environment; a humidity sensor coupled to the thermostat and operable to determine the humidity of the indoor air environment; and an air flow probe positionable downstream from the dehumidifier to sense the temperature of the air flow from the HVAC system. 